1. Field of the Invention
The present invention pertains to the control arts, and more particularly the indication of the position of a hydraulically actuated valve.
2. Description of the Prior Art
In the teeming of molten steel, refractory lined sliding gate valves are used to control the flow. Such sliding gate valves are typically hydraulically actuated, and the operator normally monitors the flow by simply watching the stream of molten steel. However, in such high temperature and corrosive environments, the accuracy of such visual inspection of flow will depend heavily in the skill and experience of the operator, and even with the most skillful operator the accuracy and repeatability of a sliding gate valve position is limited. Thus it is a problem with the prior art to accurately and repeatedly set the position of a sliding gate valve used for teeming molten steel.
The prior art also includes Davis U.S. Pat. No. 2,802,483 which discloses a mechanical valve position indicator for a hydraulically actuated gate valve. The position indicator is merely a pointer worm-geared to the valve stem. Such a mechanical valve position indicator has the usual problems with mechanical devices in high temperature and corrosive environments of ruggedness, warpage, and mechanical clearance between moving parts which limits accuracy and repeatability.
The prior art also includes Maclay U.S. Pat. No. 3,081,942 which discloses an electronic measurement of hydraulic control fluid flow as part of a digital-to-analog control device. The electronic measurement is made by counting pulses generated as the control fluid flow drives a pair of meshing gears which rotate past a magnetic transducer. However, Maclay fails to disclose any corrections to the fluid flow measurement to compensate for transients occurring when the fluid flow is stopped and restarted and to compensate for elimination and creation of mechanical clearances in the control member. Indeed, Maclay fails to even note the existence of such measurement problems.